George, I think the confusion is the 'one step back' generation thing - if you think about it it all starts with an inbalance.
By that I mean that in the first generation back you have parents, and their brothers and sisters are your uncles and aunts.
In the second generation back you have grandparents, and their brothers and sisters are your great uncles and aunts.
In the third generation back you have great grandparents, and their brothers and sisters are your great great uncles and aunts.
I do see what you mean, in that in the last example, the third generation, you have 1 x 'great' in the term for the parents and 2 x 'great' in the term for their brothers and sisters but that's because the 'great' kicks in for parents one generation later than it does for Uncles and Aunts.
That's just the way it is, and as far as I know always has been. It's normal practice - do you really think it will confuse people looking at trees? I would have thought that anyone who had the interest in the subject enough to want to see the family tree would be able to work that out.
The interchange of Great Uncle / Grand Uncle seems to be a family / culture thing, as Aghadowey says the terms are both used in America, but in Britain the majority only use the word 'Great' in that context (as far as I know.. happy to be corrected)